In recent years, as an alternative to oil resources and in connection with the growing environmental consciousness, applications of reproducible natural fibers attract attentions. Among natural fibers, cellulose fibers, especially those derived from wood (pulp), are widely used mainly for paper products. Most of cellulose fibers used for paper products have a fiber width of 10 to 50 μm. Paper (sheet) obtained from such cellulose fibers is opaque, and is widely used as paper for printing. If cellulose fibers are refined (microfibrillated) by a treatment in a refiner, kneader, sand grinder, or the like (beating or grinding), transparent papers (glassine paper etc.) are obtained from such fibers.
As an apparatus for producing a sheet containing fibers, Patent document 1 (Japanese Patent Unexamined Publication (KOHYO) No. 2012-516399) discloses an apparatus for making a nonwoven web, the apparatus comprising: a) a first source configured to dispense a first fluid flow stream comprising a fiber; b) a second source configured to dispense a second fluid flow stream also comprising a fiber; c) a mixing partition downstream from the first and second sources, the mixing partition positioned between the first and second flow streams, the mixing partition defining two or more openings in the mixing partition that permit fluid communication and mixing between the first and second flow streams; and d) a receiving region situated downstream from the first and second sources and designed to receive at least a combined flow stream and form a nonwoven web by collecting the combined flow stream, and Japanese Patent Unexamined Publication (KOHYO) No. 2012-516399 Patent document 1 describes that the apparatus may further comprise a drying section proximal and downstream to the receiving region, and the drying section may comprise a drying can section, one or more IR heaters, one or more UV heaters, a through-air dryer, a transfer wire, a conveyor, or a combination thereof.
Patent document 2 (Japanese Patent Unexamined Publication (KOKAI) No. 2012-116905) discloses a method for producing a composite porous sheet using fine cellulose fibers and a polymer having a film-forming property, which is a method for producing a fine cellulose fiber composite porous sheet comprising a preparation step of mixing an aqueous suspension containing the fine cellulose fibers with an emulsion of the polymer having a film-forming property to produce a mixture, a papermaking step of forming a sheet containing moisture by dehydrating the mixture by filtration on a porous base material, a step of substituting an organic solvent for the moisture contained in the sheet, and a drying step of drying the organic solvent-substituted sheet by heating, and mentions cylinder dryer, yankee dryer, hot air drying, infrared heater, etc. as the drying means.
Patent document 2 discloses a method for producing a composite porous sheet using fine cellulose fibers and a polymer having a film-forming property, which is a method for producing a fine cellulose fiber composite porous sheet comprising a preparation step of mixing an aqueous suspension containing the fine cellulose fibers with an emulsion of the polymer having a film-forming property to produce a mixture, a papermaking step of forming a sheet containing moisture by dehydrating the mixture by filtration on a porous base material, a step of substituting an organic solvent for the moisture contained in the sheet, and a drying step of drying the organic solvent-substituted sheet by heating, and mentions cylinder dryer, yankee dryer, hot air drying, infrared heater, etc. as the drying means.
Patent documents 3 and 4 (Japanese Patent Unexamined Publication (KOKAI) No. 2007-23218 and Japanese Patent Unexamined Publication (KOKAI) No. 2007-23219) describe a fine fiber sheet obtained by separating a dry fine fiber layer from a base material, which dry fine fiber layer is formed on the base material by applying a slurry containing fine fibers on the base material and evaporating liquid components in the slurry, and describe that hot air drying, infrared drying, vacuum drying etc. are effective for the drying.
Patent document 5 (Japanese Patent Unexamined Publication (KOKAI) No. 2008-248441) describes a fiber sheet containing cellulose fine fibers treated with a hydrophobizing agent such as a sizing agent, oil and fat, wax, and hydrophobic resin. The fiber sheet described in Patent document 5 Japanese Patent Unexamined Publication (KOKAI) No. 2008-248441 shows low hygroscopicity and thus reduced dimensional change due to moisture absorption, because it is constituted with cellulose fine fibers made hydrophobic.
Patent document 6 (Japanese Patent Unexamined Publication (KOKAI) No. 2013-71456) describes a porous sheet comprising a fine fiber web layer consisting of fine fibers having a diameter of 50 to 5000 nm, and a support layer, on one or both surfaces of which the fine fiber web layer is bonded. Further, it describes that the fine fiber web layer is formed by forming fine fibers consisting of a mixture of a polymer and an adhesive material through electrostatic spinning of a spinning solution consisting of a mixture of solutions of the polymer and the adhesive material, spraying a solution of the adhesive material on the fine fibers, and then bonding the fibers on the support layer to form the fine fiber web layer.